Rare Bird - The Sound City Concord Combo

1. The rare Sound City Concord. This dual EL34 2x12 combo even sports an output level meter.
2. Yow! This tube socket has high-voltage burn marks between the pins, so it will need to be replaced.
3. The view from behind reveals a pair of square-magnet Eminence 12s with manufacturing date
codes from 1972.

This month, rather than answer one of
your questions (which, by the way, I am
very thankful for and look forward to), I’m
going to dedicate this column to a project
that’s been on the back burner for a while.
Okay—10 or 15 years, but who’s counting?

A customer brought this amp to me for
repair and I don’t remember if it had been
given to him after it failed or if the failure
occurred while he owned it, but after seeing
the damage he decided that it was simply
not worth the effort and expense to bring
the beast back to life. Not living near a
landfill, he left it with me to use as a boat
anchor. Seeing as how I didn’t own a boat,
I initially thought I might just hang on to
it as a source of parts. After thinking on it
further, I decided to just store it away in the
hopes that someday I might scar an apprentice
for life with the task of resuscitating
this corpse, I mean combo.

Well, I never found it in my heart
to bestow this overwhelming task upon
anyone, so I’ve finally decided to take it
on myself. Ladies and gentlemen, I give
you the Concord! This rather strange and
unique combo was produced by Dallas
Arbiter under the Sound City moniker in
the late ’60s and early ’70s. Here goes my
attempt at resurrecting this rare example of
British history. Let the fun begin.

In case you’ve never seen one—and
it’s unlikely you have—the Concord is a
2-channel, 2x12 combo with reverb. Each
channel has two inputs (low gain and high
gain), volume, treble, and bass controls,
and a brilliant switch. There’s also a master
“reverb volume” control and to top it all off,
an output level meter. (I guess that feature
was added for the deaf player. Nice touch.)

Examining the speakers, I found the
square-magnet 12s were manufactured by
Eminence in the 36th week of 1972 (67-
7236), and since they appear to be the original
matched pair, this discovery should serve
to date the amp. This Concord contains a
pair of EL34 output tubes and five preamp
tubes—three 12AX7s and two 12AT7s. By
looking at the Partridge transformers, my
guess is that this is a 35- to 40-watt amp.

Covered in typical black vinyl with a
very tasty cream-and-oxblood grille cloth,
the cabinet sports some uniquely rounded
bottom corners. From a production standpoint,
this is definitely a manufacturing
irritant, yet it offers a way-cool retro vibe.

But even more unusual are this amp’s
controls, which are not your typical rotary
type. All the volume, bass, treble, and
reverb controls are sliders, and in following
the typical upside-down British design
(for example, where down is “on” for power
switches), on these sliders up is minimum
and down is maximum. And if that weren’t
odd enough, foreseeing Spinal Tap and
not to be outdone, all controls go to 12!
Because it’s one more than 11.

So much for the aesthetic—let’s see
what it takes to get this piece of history
up and running.

Upon initial inspection, I found that
the rear-panel fuse had blown. Probably a
good thing, I reasoned, as this should have
stopped any catastrophic internal failure. (I’d
soon be forced to retract that statement.)
The first suspect for a fuse failure in a tube
amp is an output tube, so out they came.
After I removed the tubes, I saw that a tube
socket had high-voltage burn marks between
the pins, so it would need to be replaced.

Okay, no problem—I’ve seen this a hundred
times. High voltage can wreak havoc
under the wrong conditions, and the base
of the tube showed the same damage, so the
amp will need a new pair of output tubes.
Replace the output tube sockets, install and
bias a new pair of output tubes, and the
amp should be good to go.

A unique feature in the circuit design
of this amp is that it has separate biasadjustment
pots for each output tube. A nice
touch, as the amp preceded the mass availability
of matched output tubes that are so
ubiquitous today. Tolerances in tube manufacturing
at that time had started to drift
(presumably from lack of equipment maintenance,
as everybody knew that tubes would
soon become obsolete and be replaced by the
transistor), and tubes were becoming less and
less matched within production runs. This
amp’s bias feature would let you individually
set the desired idle current for each tube.
Actually, it’s a much better method than the
“balance” method adopted by Fender during
this period.

So, assuming the speakers were in good
working order, I figured the cost of replacing
the sockets and installing new tubes
would be reasonable enough to prevent this
amp from becoming a doorstop. I decided
to proceed as normal with the repair.

When I continue next month, you’ll get
to see what I found when I pulled the chassis!
Jaw-dropping to say the least. See you then.

Jeff Bober is one of the godfathers of the low-wattage amp revolution. He co-founded and was originally the principal designer for Budda Amplification, though he launched EAST Amplification (eastamplification.com) in 2010. You can catch his podcasts at ampsandaxescast.com or email him at pgampman@gmail.com.

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